A new model presents more evidence that these mysterious features are build by underground architects.
A new twist on an old mystery may finally settle the debate over the origin of Mima mounds, which bulge out of the ground like enormous, grass-covered bubble wrap.
Mima mounds (sounds like dime-a) were named in 1841, when a vast pimply prairie (the Mima Prairie) was discovered in western Washington during the United States Exploring Expedition. In the centuries since, the source of this strange landscape has defied explanation. A single field may be covered in a million mounds that are several thousand years old, yet no builder has ever been found.
But now, a study strongly suggests that one of the prime suspects, pocket gophers, are indeed the builders.
The model suggests that gophers start pushing soil toward any existing high spots, and these budding mounds continue to beckon later generations of builders. “There’s a positive feedback where the gophers are somehow sensing where the high spots are,” Gabet said.
Eventually, the burrowing mammals run out of soil and the Mima mounds are fully “developed” — which takes 500 to 700 years.
The problem has always been that we could not see the gophers building them. Another unique feature of areas of mima mounds is a layer of clay that is impenetrable to water. So, the gophers, to avoid getting drenched, need to build upwards to avoid it. Curious stuff. While the study is not proof that it is gophers, its making more sense now that this is the most plausible explanation.
Mima mounds have been a perpetual mystery, appearing in books on natural anomalies. Other theories of how they were formed included wind or seismic activity or the behavior of the swelling clays in the soil.